Method of distilling lubricating oils



Dec. 28, 1937. F. lc5. FELLows 2,103,898

METHOD OF DISTILLING LUBRICATING OILS Filed April 11, 1932 2 sheets-sheet 2 anys.

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ATTORNEY.

Patented Dec. 28, 1937 UNITED STATES 2,108,898 METHOD oF DIS'ILISING LUBRICATING Fred G. Fellows, Ponca City, Okla., assignor to ,Y

Continental Oil Company, Ponca City, Okla., a corporation of Delaware Application April 11, 1932, Serial No. 604,441

1 Claim.

My invention relates to a method of distilling lubricating oils and more particularly to a method of distillation for increasing the neutral yield, and parafn wax yield.

Vacuum distillation and ash distillation at atmospheric or super-atmospheric pressures have been resorted to in order to produce overhead lubricating oils of high physical `qualities from inferior crudes leaving the tars and asphalts as a residue which is withdrawn from the bottom of the fractionating column as a heavy flux.

In order to secure the highest yield in quality of heavy lubricating oil distillate ranging in general from a viscosity of 125 seconds to 210 seconds at 210 F., it is necessary that the distillation be made at a reduced temperature or at reduced effective partial pressures. This is secured by vacuum distillation or by the use of large quantities of steam during the distillation at atmospheric pressures to strip the lubricating fractions from the heavy material. This distillate is used subsequently to manufacture cylinder stocks and bright stocks. v

The light lubricating oil distillate or Wax distillate has a viscosity range varying in general from 40 seconds to 140 seconds at 100 F.

, In order to secure a satisfactory dewaxing of this distillate, especially for low cold test oils, it is necessary that, in case of the light lubricating oil distillate, the stock be prepared with a minimum amount of amorphous or micro-crystalline wax. When a heavy lubricating oil distillate is removed to use in the manufacture of a heavy or high viscosity lubricating oil, it is desirable that a minimum amount of crystalline Wax be present.

This is due to the fact that different processes are used to dewax respective light and heavy v fractions after distillation, which will be hereinafter more fully discussed.

In the preparation of a Wax distillate with good pressable and sweatable characteristics, itis necessary rst that asphalt and resinous compounds be removed inasmuch as their insolubility will persist with wax and interfere with crystallization and purification; secondly, that the viscosity of the lubricating oil which forms the bulk of the wax solvent be reduced sufficiently to admit of a practical separation by the conventional chilling and lter pressing methods. y

When`fractional distillation is carried out under a vacuum or at atmospheric pressure, accompaniedby steam stripping it has been found that with many crudes it is impossible to include in the light lubricating oil distillate or wax distillate a certain fraction, the boiling range of which lies immediately below that required for the heavy lubricating oil distillate, for the reason that this fraction contains some amorphous or microcrystalline paraffin Wax and the oil solvent is so vis- 5 cous that the Wax does not crystallize on chilling into readily fllterable crystals. The increased content of asphaltic compounds in these higher boiling fractions amplifies this effect. It would,

therefore be necessary in the present type of operation to withdraw this fraction as a separate side stream from the fractionating column. The viscosity range of this fraction is generally'from 40 seconds to 110 seconds at 210 F. It is generally referred to in the industry as a slop cut or which might, if not separated, hinder the formation of crystalline wax.

Heretofore, the practice in the industry, when it is desired to convert this slop cut into a pressable and sweatable Wax distillate is to charge the oil to a conventional batch shelll still operating at or slightly above atmpspheric pressure, and then subject the oil to a thermal treatment at temperatures ranging usually' from 600 F. to 700 F. The slop cut so treated is generally referred to as a cracked Wax distillate. 'I'his proc- 35 ess is generally carried on as a distillation process without fractionation, taking overhead first the gas oil fraction, then a cracked wax distillate fraction and leaving approximately 10 to 12 percent of the original charge in the still as a residue, 40

consisting chiefly of resinous or asphaltic com-l pounds.

In dewaxing fractions recovered from the distillation of oils in the process of making lubricating oils, two general vmethods are employed, namely the lter press method and the centrifugal or cold settling method.

The filter press method is used for dewaxlng those light lubricating oil distillates which are generally referred to as wax distillates and which contain parain wax in the formof well defined crystals. The paraflin wax on being passed through a filter press, collects on the press blankets. This wax is removed in sheets and subjected to a sweating `process to reduce the oil and cation embodying my invention.

moisture content. The light lubricating oil separated from the wax in the present process is the base of light oils generally referred to as neutrals. i

The centrifugal or cold settling methods are used for dewaxing the heavy lubricating oil distillates in which the parafln wax is present in an amorphous or micro-crystalline system, gen'- erally referred to as petrolatum. The amorphous Wax is separatedj by chilling and centrifuging with a material which will form nuclei for the iiocculation of the amorphous wax.

One object of my invention is to provide an economical and efficient process for treating a slop cut to convert a large portion thereof into a pressable wax distillate of high quality.

Another object of my invention is to provide a process for increasing the total yield of wax distillate from a lubricating 'oil distillation unit.

A further object of my invention is tn provide a process for increasing the total yield of neutral oil from a lubricating oil distillation unit, as well as the yield of paraiiin waX.

Still another object of my invention is to provide a process for improving the general quality of cylinder stock obtained from a' lubricating oil distillation unit.

Other objects of my invention will appear from the following description.

In general, my'invcntion consists in that improvement over the present vacuum and. flash distillation operation in which the slop cut is withdrawn from the fractionating column and is pumped through heating tubes located in the furnace of the distillation unit or, if desired, through a separately fired furnace. It is to` be understood, of course, that a high temperature heat exchanger may be used in order to heat the slop cut-to its wax cracking temperature. The slop cut thus withdrawn and heated is given a thermal treatment or cracking at temperatures which Will vary from 600 F. to 800 F. at atmospheric pressure or the equivalent thermal treatment at pressures above or below atmospheric.

The vapors from the heating or wax ycracking operation are then discharged into the fractionating column for refractionation.

In the drawings:

Figure 1 shows a diagrammatic view of one method of carrying out my invention.

Figure 2 is a diagrammatic view of a modifi- Figure 3 is a .diagrammatic view of an apparatus capable of'carrying out another. modication of th@ process of my inventioni Figure 4 is a diagrammaticview of still another method of carrying out the process-of my invention.

More particularly referring now to the drawings, a topped crude isJ charged through line .I, through pump 2, through heating cbil 3 of the furnace 4 and heated to vaporiz'ing temperatures. The vapors leave the furnace 4 through line 54 and are flashed into fractionating tower 6 maintained under subatmospheric pressure by any suitable vacuum equipment 'I. It is to be understood, however, that an atmospheric fractionating tower using stripping steam may be employed.y The vapors undergo their usual fractionation in the fractionating tower which may be of any suitable type. The head products leave the fractionating tower through line 8 and pass through cooler 9 and are withdrawn as 'gas oil through line I0. The wax distillate is withdrawn from.

the fractionating tower through line il passing through cooler I2 and leaving through valve controlled line i3. .A reiiux line I4 is provided through which pump I5 may pump the wax distillate for reintroduction into the tower. The heavy residue is withdrawn from the bottom of the fractionating tower through line I6 and is passed through its cooler I1. The usual stripping section 1B is provided in the bottom of the fractionating tower 'into which steam through line I9 is introduced for stripping the lighter fractions from the heavy residuum before it is withdrawn. Heavy cylinder stock containing chiefly amorphous wax is withdrawn through line 20 and is passed through cooler 2I to storage.

The slop cut, that is the fraction whose viscosity range is between seconds and 110 seconds at 210 F. and which contains some amorphous and some crystalline wax is withdrawn through line 22 and pumped through valve controlled line 23 by pump 24. If desired, a portion of this fraction may be withdrawn through valve controlled line 2.5 and passed through cooler 26 to storage.

It will be noted that in the four modifications hereinafter shown and appearing in Figures 1, 2, 3, and 4 of the drawings, the above operation is common. In other words, the operation of my process is the same in all four modifications tothe point where the slop cut is withdrawn from the tower. v

Referring now to Figure 1, the pump 24 pumps the slop cut through line 21, through heating coil 28 in which the slop cutis heated to temperatures ranging usually from 600 F. to '700 F. The cracked slop vapor leaving coil 28 through line 29 is introduced intoth line 5 which conducts the topped crude vapors to the fractionating tower. In carryingout this modication of my invention, it is necessary that the topped crude vapors leave the furnace at a reduced temperature in order that, after admixing the slop cut vapors therewith, the combined temperature at which ashing occurs is such that no cracking of thevaluable heavy lubricating oil hydrocarbons occurs.

Referrlng'now to Figure 2,-the pump 24 pumps the slop cut through line 21, through heating heavy lubricating oil fractions from the flux bottoms.

With reference now to Figure 3 which I have found to be the better method ,of operating, I pump Ithe slop cut through line 21 and heating coil 28 as before. The cracked slop vapors leaving the heating coil 28 through line 29 are introduced to a stripper column 30 in which the compounds of a resinous, colloidal or asphaltic character are separated and withdrawn from the bottom of the stripping tower as a heavy t`ar or nux. `The vapors enter the stripping column 3|! where they are stripped withst'eam which enters through valve controlled line 3 I. The heavy residue is withdrawn through valve controlled line 32 which discharges into line I6 through which the bottoms o f the fractionating tower flow to the cooler I1. The head product from the slop stripper passes through line 33. A portion ofA the head product is diverted throughline 34, passed-through cooler 35, through valve conmain fractionating column 6 preferably under the slop drawoi tray where they add additional dry heat within the tower and serve as a stripping medium.for the slop oil fractionating section. This `additional supply of heat makes it necessary to use larger quantities of reux at l the top of the wax distillate fractionating section thereby securing a better fractionationl of this product. By the use of this method a lower transfer temperature can be maintained for the topped crude vapors entering the tower. This results in a reduced decomposition of the heavy lubricating oil hydrocarbons.

Referring now to Figure 4, the method there shown is similar to that shown in Figure 3 except that the entire head product leaving the stripper 30 through line (i3v is passed through cooler and collected in reux accumulator 31. The pump 3B pumps the condensate which serves as an intermediate reux, through line 4I into line 42 for discharge into the tower for securing additional refiuxing with the resultant improvement of fractionation in the slop oil fractionating section.

The total overhead vapor in this method is cooled to approximately the same temperature as the vapors in the slop oil fractionating section of the main fractionating column to which they are discharged under equilibrium conditions through line IZ. In the method according to Figure 4 a higher transfer temperature is required. This is objectionable from the standpoint of heavy lubricating oil quality and yields. This method, however, would be desirable if a maximum yield of light or wax distillate is desired, rather than a heavy lubricating oil. Provision is made for recycling a portion of the condensate as a control reiiux into the slop stripper through line 42'.

It will be obvious that my method has many during the distillation makes the process a continuous one of an increased thermodynamic eciency.

It will be appreciated that I have accomplished the 'objects of my invention. It will be understood that certain features and sub-combinations are of utility and may be employed-without reference to other features and subcoml:inations.y

This is contemplated by and is within the scope of my claim. It is further obvious that various changes may be made in details within the scope of my claim without departing from the spirit of 'my invention. It is, therefore, to be understood that my invention is not-to be limited to the specific details shown and described.

Having thus described my invention, what I claim is: l

A process of distilling hydrocarbon oils including heating a wax bearing hydrocarbon oil to distillation temperatures, flashing the heated oil into vapors and unvaporized oil in a fractionating zone, withdrawing the unvaporized oil from the process, fractionally condensing the vapors in the fractionating zone, withdrawing reflux condensate containing amorphous wax from the fractionating zone, heating a portion of the amorphous wax bearing condensate to wax cracking and vaporizing temperatures whereby a portion of the amorphous wax is converted into vapors containing wax which, upon condensation, will form wax crystals having pressing qualities, separating the thus heated amorphous wax bearing condensate into vapors and unvaporized oil in a second fractionating zone, withdrawing the unvaporized oil from the process, condensing the vapors and introducing the condensate containin'g pressable wax into the first fractionating zone as an intermediate reflux, and withdrawing reflux condensate containing pressable wax from said fractionating4 zone.

FRED G. FELLOWS. 

